Gas turbines are widely used in industrial and power generation operations. A typical gas turbine may include a compressor section, a combustion section disposed downstream from the compressor section, and a turbine section disposed downstream from the combustion section. A working fluid such as ambient air flows into the compressor section where it is progressively compressed before flowing into the combustion section. The compressed working fluid is mixed with a fuel and burned within one or more combustors of the combustion section to generate combustion gases having a high temperature, pressure, and velocity. The combustion gases flow from the combustors and expand through the turbine section to produce thrust and/or to rotate a shaft, thus producing work.
The combustors may be annularly arranged between the compressor section and the turbine section. In a particular combustor design, the combustors include one or more axially extending bundled tube fuel injectors that extend downstream from an end cover.
The bundled tube fuel injector generally includes a plurality of pre-mix tubes arranged radially and circumferentially across the bundled tube fuel injector. The pre-mix tubes extend generally parallel to one another. An outer shroud extends circumferentially around the pre-mix tubes downstream from a fuel distribution module of the bundled tube fuel injector. An aft plate extends radially and circumferentially across a downstream end of the outer shroud adjacent to a combustion chamber or zone defined within the combustor. A cooling air or purge air plenum is at least partially defined within the outer shroud between the fuel distribution manifold and the aft plate. In a conventional bundled tube fuel injector, a downstream or end portion of each pre-mix tube extends through the aft plate such that an outlet of each tube is downstream from a hot side surface of the aft plate, thus providing for fluid communication into the combustion chamber or zone.
Each of the pre-mix tubes extends generally axially through the fuel distribution module and the cooling air plenum. The compressed working fluid is routed through inlets of each of the parallel pre-mix tubes upstream from the fuel distribution module. Fuel is supplied to the fuel plenum through the fluid conduit and the fuel is injected into the pre-mix tubes through one or more fuel ports defined within each of the pre-mix tubes. The fuel and compressed working fluid mix inside the pre-mix tubes before flowing out of the outlet which is defined at the downstream or end portion of each of the pre-mix tubes and into the combustion chamber or zone for combustion.
During operation of the combustor, the downstream or end portion of the pre-mix tubes is exposed to extreme temperatures due their proximity to the combustion chamber and/or the combustion flame. Over time, the downstream or end portion of the pre-mix tubes degrades due to the thermal stresses, thus requiring scheduled inspection and in some cases repair or refurbishment of the bundled tube fuel injectors. Materials that are suitable for high or extreme temperatures and that may enhance the life of the pre-mix tubes are relatively expensive. As a result it may be impractical and/or cost prohibitive to manufacture the pre-mix tubes entirely from these materials. Therefore, an improved bundled tube fuel injector would be useful.